1. Technical Field
An air temperature and humidity control device using a liquid-desiccant humidity controller thermally coupled to a heat pump is disclosed. The humidity controller includes a contactor having at least one contact module with a porous sidewall that is permeable to water vapor and impermeable to the liquid desiccant. The disclosed device controls air temperature through heat transfer between the liquid desiccant and heat pump and controls humidity through water transfer between the desiccant and surrounding air.
2. Description of the Related Art
Conventional air conditioning systems generally do not perform humidity control functions. In case humidity control is desired, air conditioners based on direct expansion (DX) may be operated to condense moisture in the air through supercooling. The drier, supercooled air is then reheated for comfort before entering into a facility to be air-conditioned. Significant energy is consumed during the supercooling and reheating, which renders the process inefficient. Moreover, water condensation on metallic DX coils may cause corrosion problems, which adds to the maintenance cost of the air conditioning systems.
In light of the need for more efficient humidity control, air conditioning systems with desiccant wheels separated from temperature control units have been developed. The desiccant wheel is loaded with a solid desiccant and is positioned just downstream of the temperature control unit so that cooled air transversely passes a ¾ section of the rotating desiccant wheel, during which the moisture in the air is absorbed by the desiccant. The remaining ¼ section of the desiccant wheel is reheated so that the absorbed moisture can be desorbed to regenerate the desiccant. While capable of achieving low humidity outputs, systems based on desiccant wheels may be space-consuming and may suffer from lack of efficiency, as heating energy is required to regenerate the desiccant. Moreover, because the desiccant wheel is relatively cumbersome and not easy to install or uninstall, the capacity and operation of the systems based on desiccant wheels are generally not modular enough to accommodate a wide range of operations.
Besides desiccant wheels, humidity control may be achieved with an air conditioning system having a heat pump coupled to a liquid desiccant loop so that the liquid desiccant, such as lithium chloride, can be cooled and heated by the heat pump. The desiccant loop includes two contact towers loaded with packing materials. Several sprinklers are provided at the top end of the tower to distribute the liquid desiccant (cooled or heated by the heat pump) onto the packing materials, while air is blown from the bottom end of the contact tower as the liquid desiccant trickles down the packing material. As a result of the direct contact between the desiccant and air, water may be absorbed from the air into the desiccant or desorbed from the desiccant into the air. Simultaneously, the air may be heated or cooled by the liquid desiccant.
Because of its integration with a heat pump, the liquid desiccant system discussed above requires less energy for the desorbing of water from the liquid desiccant, i.e. the regeneration of the liquid desiccant. However, as the operation of the system requires direct contact between numerous streams of liquid desiccant and air, significantamount of noises, e.g. bubbling noise, are generated by the system, which may disturb the ambience of the room or facility that is the subject of the system. The entrainment of liquid desiccant droplets into the air stream is inherent to spraying direct contact technologies. Such liquid desiccant entrainment (or liquid desiccant carryover) can cause corrosion of ductwork and human health issues. Moreover, similar to the desiccant wheels, the contact towers of the above-discussed system is relatively cumbersome in construction and not easy to modulate to accommodate a wide range of operations.
Hence, there is a need for an air conditioning system with humidity control capabilities. Moreover, there is a need for an air conditioning system that achieves humidity control in an energy efficient and discreet manner. Finally, there is a need for an air conditioning system with modular humidity control to conveniently accommodate a wide range of operational needs.